DNA sequencing is one of the most important analytical methods in modern biotechnology. Detailed reviews on current sequencing technologies are provided in M. L. Metzker, Nature Reviews 2010, 11, 31 [1], and C. W. Fuller et al., Nature Biotechnology 2009, 27, 1013 [2].
A well-known sequencing method is the Sequencing-by-synthesis (SBS) method. According to this method, the nucleoside triphosphates are reversibly blocked by a 3′OH-protecting group, in particular esters and ethers. Examples for esters are alkanoic esters like acetyl, phosphates and carbonates. The nucleoside triphosphate usually comprises a label at the base.
A method of enzymatically synthesizing a polynucleotide of a predetermined sequence in a stepwise manner using reversibly 3′OH-blocked nucleoside triphosphates was described by Hiatt and Rose (U.S. Pat. No. 5,990,300) [3]. They disclose besides esters, ethers, carbonitriles, phosphates, phosphoramides, carbonates, carbamates, borates, sugars, phosphoramidates, phenylsulfenates, sulfates and sulfones also nitrates as cleavable 3′OH-protecting group. The deprotection may be carried out by chemical or enzymatic means. There are neither synthesis procedures nor deprotection conditions and enzymatic incorporation data disclosed for the nitrate group. The claimed deblocking solution preferably contains divalent cations like Co2+ and a biological buffer like Tris. 3′OH-blocked nucleoside triphosphates containing a label are not disclosed.
Buzby (US 2007-0117104) [4] discloses nucleoside triphosphates for SBS which are reversibly protected at the 3′-hydroxyl group and carry a label at the base. The label is connected via a cleavable linker such as a disulfide linker or a photocleavable linker. The linker consists of up to about 25 atoms. The 3′OH-protection group can be besides hydroxylamines, aldehydes, allylamines, alkenes, alkynes, alcohols, amines, aryls, esters, ethers, carbonitriles, phosphates, carbonates, carbamates, borates, sugars, phosphoramidates, phenylsulfanates, sulfates, sulfones and heterocycles also nitrates.
What is needed in order to achieve longer read length and better accuracy in nucleic acid sequencing is a nucleotide analogue with a cleavable protecting group and a cleavable linker which do not leave reactive residues after cleavage [5].